In general, semiconductor-based light sources such as light emitting diodes (LEDs) and semiconductor diode lasers have relatively narrow spectral outputs. There is a need, however, for devices with a broad spectral output for applications such as fiber-optic gyroscopes, chemical sensors, wavelength division multiplexing communications systems with passive drops, and displays. Attempts to achieve broad spectral outputs from diode lasers have generally either incorporated a number of quantum wells into the active regions of the device, or used high excitation levels to achieve transitions from more than one quantized level in combination with other broadening mechanisms that occur at high carrier densities. Generally those schemes, however have been implemented in edge emitting designs which result in significant costs due to the need to handle and package individual chips. The recent development of vertical cavity surface emitting lasers (VCSELs) which incorporate a resonant cavity produced using quarter wave Bragg mirror stacks has resulted in the demonstration of lasers that emit perpendicular to the substrate, alleviating many of the packaging and handling problems associated with diode lasers and reducing the operating current as well. VCSELs are inherently single frequency sources, however, and LEDs fabricated using structures similar to VCSELs have narrow spectral outputs as well. Thus there continues to be a need for a surface emitting light source with a broad spectral output.
It is the purpose of this invention to provide a new design for a surface emitting light emitting diode with broad spectral output and high efficiency.